1. Field of the Invention
The present invention relates to a power-on detector. More particularly, the present invention relates to a power-on detector with temperature immunity.
2. Description of Related Art
In many electronic devices and circuits, a power-on detector is generally used to detect whether an external power is turned on. For example, when a supplied power is increased to a threshold value of 1 volt (V), the power-on detector then determines the power is turned on. However, in allusion to design requirements of energy-saving and processing of consumer products, the threshold value becomes smaller and smaller, and a processing size also becomes smaller and smaller. Now, a circuit of the power-on detector can be influenced by temperature, so that whether the power is turned on can be misjudged. The conventional power-on detectors are categorised into two types of a bandgap type and a P/N device+resistance type. FIG. 1 is a diagram of a conventional bandgap type power-on detector. When an input voltage Vcck is provided, the bandgap type power-on detector 100 determines whether the power is turned on according to a difference between a positive end voltage Vpos2 and a negative end voltage Vneg2. Though the difference is less influenced by the temperature, the difference itself is quite small, for example, 13.99 mV, so that, the power-on detector 100 can make a false judgement due to a device variation generated under a 65 nanometer processing.
FIG. 2 is a diagram of a conventional P/N device+resistance type power-on detector. When the input voltage Vcck is provided to the P/N device+resistance type power-on detector 200, the power-on detector 200 determines whether the power is turned on according to a difference between a positive end voltage Vpos3 and a negative end voltage Vneg3. The difference between the positive end voltage Vpos3 and the negative end voltage Veng3 can be changed along with the temperature. For example, the difference of (Vpos3−Vneg3) can be 142.8 mV under −40° C., and can be 21.08 mV under 125° C., so that a determination result of the power-on detector 200 can be greatly different under different temperatures.